The invention relates to a method for forming stacks of specific length, which can vary, using upright positioned and successively lined up signatures. The signatures are supplied one after another with a conveying system from a printing press to a stack-forming device where the signatures are separated into individual stacks by a separating device.
The invention furthermore relates to an arrangement for realizing such method.
One skilled in the art will also refer to stacks of the aforementioned type as bundles and to the stack-forming device as a bundle delivery device. Stacks of this type are formed in particular on offset printing as well as sheet-fed photogravure rotary machines, wherein the stacks are formed inside the stack-forming device. The signatures to be stacked are supplied with transport belts to the stack-forming device. In the stack-forming device, the signatures are pushed together while positioned on the bound edge. During the further processing, the signatures are pulled off, for example, in a feeder for a gathering and wire-stitching machine and perfect binder, so that book blocks can be produced with these signatures.
Devices for forming such stacks are described, for example, in European Patent Documents EP 0 623 542 A and EP 1 199 275 A, identified above, which describe methods and systems to compress and strap the stacks. A device for palletizing the compressed and strapped stacks is described, for example, in European Patent Document EP 1 378 472 A, identified above. For suitable palletizing and further processing, the stacks are typically required to have a specific length, for example, in the range from about 500 to about 1200 mm.
The signatures to be stacked are produced, for example, in a rotary or digital printing press, which can operate at extremely high capacities. Such machines can switch quickly from a production A to a production B, for example, with a plate change. The different productions are separated inside the stack-forming device. Stacks containing items from both productions A and B might not be tolerated. Therefore, the stacks should comprise only items from one production, thus making it necessary to have a separation between the stacks composed of different production items. Until now, this has been achieved with a comparably high accumulation of waste materials at the end of the production run. Additionally, a comparably long period for the changeover has been required between different productions, since the conveying system at the end of a production contains remaining items which cannot be used to form a stack. Such items are either treated as waste material and are discarded or such items are transferred out and subsequently placed manually onto a pallet. Thus, in the systems available today a manual intervention is required before the start of each subsequent production, which might result in a comparably long changeover time.
The described problems are especially prominent when printing small editions such as paperbacks and other books or print products. The small editions impose especially high requirements for a cost-effective production. To lower the costs, it is particularly important with the small editions to prevent the unnecessary accumulation of waste and avoid manual operations.